<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="elem" about="Elephant"></div>

  <script>
    console.log(elem)

    console.log(elem.getAttribute('About'))
    
    elem.setAttribute('Test', 123)

    console.log(elem.outerHTML)
    
    for (let attr of elem.attributes) {
      console.log(`${attr.name} = ${attr.value}`)
    }
  </script>
</body>
</html>